Secrecy signaling system



July 10, 1928.

A. CARPE SECRECY SIGNALING SYSTEM Filed Aug. 12, 1926 INVENTOR ville/m Car 100 A TITORNE Y Patented July 10, 1928.

, ALLEN CAItPE, OF NEW YORK, 11'. Y., ASSIGNORTO. AMERICAN TELEPHONE AND TELE- GRAPH COMPANY, A CORPORATION OF NEW YORK.

- SECRECY SIGNALIIIG SYSTEM.

Application filed August 12, 1926. Serial-No. 128,790.

No. 755,075, filed December 10, 1924, and to my application, Serial No. 128,7 89, filed Aug. 12, 1926.

In this invention I take a signal such as a speech signal, in which the frequency range is from about 100 to 5,000 cycles, an break it into segments or elements Spreferably ofequal length). Alternate e ements which may be taken as a group are then appliedto a device which lengthens the duration of each element and decreases each frequency and the frequency band, occupied correspondingly. The other alternate elements making a group are also modified so as to occupy a narrower frequenc band, preferably adjacentto but not over apping the band of the first group of elements. In

particular, in the case of normal speech messages, I find it advantageous to reduce all frequencies of the first group ,by the factor 2 so that this group ma then occupy a fre tpiency band 'correspon ing substantially'to t e lower halfof the original frequency band, while the second group has its frequency band width also reduced b the factor 2, but this band isso shifted by modulation as to. occupy the upper half of the original frequency band. The two resulting bands are now superposed and transmitted to, a receiving station at which the reverse process takes lace. The complex' wave is separated by ters into its components in se arate paths. The component which was shiftedby modulation is shifted back and the elements of the two portions are exanded to normal frequencies and frequency and width, and the .elementsare brought together in propertime relation to yield the original signal wave.

In the descriptionwhich follows there will be occasion to make frequent referen'ces to the change of a frequency band width and also to. a shifting of .a frequenc band.

. These two operations are distinctly ifierent in character. As-explained, for example, in' the applications referred to above, a normal speec or music signal is a complex wave d has been altered by the factor frequency bands which will be shifted with, respect to the original band by an amount with the transmitting station of Fig. 1;

made up of numerous frequencies extending from about 100 to 5,000 cycles. Such a sig nal thereforeis said to-occupy a frequency band from 100 to 5,000. By means of the Doppler principle it is possible to change each and all of the frequencies in such a band by any desired factor, such as the factor in which case are resulting signal would occupy a band from to 2,500 cycles, and it will be apparent that while there has been a slight change in position of the frequency band, the important change has been in the width of the frequency band which It is such'a change as this which is referred-to as reducing the frequency band width. On the other hand, if a normal speech signal is combined by modulation with a carrier freuency, there will then result modulation equal to. the frequency ofathe carrier, but the width of one of these modulation bands willbe unaltered; and it is such a change as this'which will be in mind when reference is made to the shifting of a frequency band;

The invention will be better understood by reference to the following description and the accompanying drawing, in which Figure 1 illustrates a circuit arrangement for a transmitting station which is to carry out the distortion mentioned above; Fig. '2 illustratest-he circuit elements and connections .for a receiving station to co-operate Figs. 3 and 4 show particular forms which the transmitting and receiving conversion devices may take on; Fig 5 shows another form of such device; and Fig. 6 shows how the invention may be applied to radio signalmg.

Referring more particularly to Fig. 1, LW may be taken to represent a path over which a normal speech signal ma travel,

the speech signal being made up 0 all fre- 100 quencies from about 100 to 5,000 cycles, and

' it will be convenient to represent any .of I

these frequencies'by f and understand that they'start from about zero. The incoming wave is allowed to pass over some formof 105 path such as the circular path 10. A djacent to said path 10 is a pickup dev ce A, adapted to reproduce the signal wave as it travels along the element 10, and to trans- I mit this signal through brush contacts to 110 the line L If this pick-up device A is stationary, it is apparent that the whole signal wave entering upon will be relayed to the line L with no changes in form.

, On the other hand, if this device A is mount ed to rotate about the center of the circuit 10, this will no longer be true. Let us suppose, for example, that the velocity of transmission of the wave along the element 10 is' V and that the velocity of the pick-up device A is in the same direction and is equal to V/2. Consideration of the figure will then show that in one complete revolution of the element A there will be transmitted to the line L, an element of the message Wave which would occupy half the circumference the L and it will its position with respect to A,"it will pick up 'the elements of the messa' e which are on t 'nients of the original message, the frequency of the path 10, and that this segment or element will now be spread over a length corresponding to one complete circumference of path 10. The duration of this element 4 therefore has been doubled and each frequency in it will have been halved so that its band extends from substantially zero to 2 500.

It is to be observed that when the element A has made one complete revolution it skips to the be inning of the path 10, and the portion of t e'message which at that moment preserved, I provide'in this invention a sec ond pick-up device B, similar in every respect to the device A, and adapted also t0 rotate in the same manner but displaced by an angle of 180 degrees. This element B is connected b suitable contacts to a line be apparent that by virtue of skipped by A, and there wil thus appear 1e lines L and. L fragments-or: eleband width for each of these fragments being one-half of that normal to a speech signal. This has been indicated on these lines by tlielegend OF/2, where it is un- 'd'erstood that F is the maximum frequency considered in the'speech signal.

' In order to maintain the integrity of these two-groups for later composition it is now necessary-to shift the frequency band of at' least one of the grou s, thus placing itjin a different portion o the frequency' spectrum. f This I may accomplish in my invention by modulating one of the groups, such as that arriving on the line L to a carrier frequency. In the figure then there is shown a modulator M which is supplied by a sustained carrier frequency F/2 from an oscillator O. The output of this modulator is then permitted to pass through a band pass filter which transmits the higher side band extending, as is obvious from F/2 to F. -The waves from the two paths may now be superposed and transmitted to a remote station, and it will be seen that the signal from the line L occupies the lower half of the frequency band of the original message,

whereas the si nal from the line L occupies the upper ha f of the original frequency band. In this circuit it 'may be desirable to place a wave filter 15 which transmits a band extendin from zero to F.

It will now e seen that there is sent out on the transmission line a signal made up of ,the original message chopped intosections,

and these' sections altered as to frequency and superposed, the whole resulting in a wave so distorted as to be beyond recognition with ordinary receiving apparatus. In Fig. 2, however, there is shown a receiving station R adapted to co-operate with the transmitting station T to correct for this distortion. To this end there is introduced in the path of the signal a band pass filter 16 adapted to pass frequencies from O to F/2, such signals passing over the path L and through suitable contacts to a recording device A. A band filter 17 is also introduced in thecircuit, this filter being adapted to pass all frequencies from F/2 to F. Since it-is necessary to bring this band of frequencies to its demodulated condition,

it is shifted by a demodulating device DM Y which is supplied by the incoming signal and by an oscillator of frequency F/2. A

.band pass filter 19 is then supplied, adapted to pass one side modulationband only, this being th'band extending from zero to F/2, after which the resultant wave pas'ses'over the line L, through suitable. contacts torecorder B. v The recorders A and B are parts of a converter which is similar to the converter of the transmitting station'T and consists of a path 20 adapted to receive and propagate impulses from the recorders A and B. Consideration of this figure will make it evident that if the velocity of propagation of the wave in the patli20 'isV, and the rotation of the elements A and B, which are 180 apart, is in the samedirection and nnmerically equal to V /2', then thefrequencies transmitted bythepath -20 ,-to the line LE I Will'be double: the frequency of the Wave coming in .onthe recorders,and therefore,

of normal si also that eac element'of signal given to the so that gaps will occur between each element.

a1 frequency. It will be-s'een line LE by A will be of half duration only," v

this time relationship, it is necemary that the arms A and B shall rotate at exactly the same rate as the arms A and B; in addiuon it is necessary that the arms A and B shall be in phase with the arms A and B, due allowance being made for the time of transmission of the signal from the path to the path 20. In other words, the two rotating arms must be run in synchronism, and for this purpose any of the well-known synchronizing means may be used.

In the above description it is stated that the oscillation of'Fig. 1 shall give the frequency F/2. It may equally well be set to give the frequency F, in which case the lower side band extendingfrom F to F /2 would be preserved for transmission bytheband filter. In this event also the oscillator of Fig. 2 should be run at the frequency F in order to yield the restored signal fragments. It will e noted that the lower side band carries with it frequency in version and thus even greater confusion in the distorted wave with accompanying greater secrecy.

. While this invention has been terms of halving and doubling thewfrequency band width, it is to be understood that this is for simplicity in the description only and that the invention is not to be limited to any such factor, but that the rotating parts,

of the converters may have a velocity bearing any desiredrelation to thevelocity of propagation along the paths 10 or 20.

The paths 10 and have been deicribed' in general terms only, this for the reason that they may take on a variety of forms such as are mentioned and described in the application of French and Zinn and in my application, both referred to above. Specifically, however, the converters may take on the form shown in Figs- 8 and 4, the first of these beingsuitable for a transmitting station and the second for a receiving station.- Referring more particularly to Fig. 3, for example, the incoming wave from the line LW may be connected to a magnetic recorder comprising a coil adjacent to an iron or steel tape or wire 31, moving wit-h any desired velocity V and in part passing around cular ath ma be mounted an arm carrying in the same direction as the tape at any suitable velocity such as V/2. Under these conditions the coils A and B will pick up elements of the message and transfer them'to the linesL, and L in the manner described "in connection with Fig. 1.

described in a circular path. At the center of this'cir-x .repr u'cing evices A and B and rotating Referring to Fig. 4, the separated received signal fragments coming over the lines L and L, will passto the recording coils A and B which are synchronously rotated about the center of a circle consisting of an iron or steel wire or ta e 20. This tape or wire 20 should be trave ing in the same direction as that of the recordersA' and B, and to follow the illustration thus fargiven,

with a velocity twice that of the velocity of the recorders. The wire tape, with its impressed signal, now in undistorted form, may pass under a reproducer 40 which picks up the signal to transmit it over the line LE. In both Figs. 3 and 4 it will be necessary to restore the magnetic tape; or wire to normal condition, and magnetizing means 32 and 42 may be provided for this purpose, or if preferred, the direct current sources may be replaced by A. C. sources as indicated by the dotted lines.

Still another form which the paths 10 and 20 may take is shown in Fig, 5. Here the transmission line LW comprises a pair of conductors which are connected to a. re-

tarding transmission path represented as a thus permitting propagation of the wave in one direction and yielding no reflection. Obviously the pick-up devices will be of appropriate type and the time relations given in connection with Figs. 3 and 4 would apinstead of the m ving tape of Figs. 3 and 4, it is apparent hat any movingerecord with suitable pick-up devices may used. One might, for example, use a photographic record or a phonograph record in a number of ways which will be obvious to those skilled in the art.

While the invention has been described in connection with a wire transmission circuit, it will be apparent that it may housed in other cases also, such as radio transmission. It would be obvious, for example, that one might take the distorted signal at the transmitting station T, just prlor to its entering the filter 15, and use it to modulate a carrier frequency for radio transmission, and that a. corresponding demodulation could be introduced at the receiving station. Another way in which the invention may be applied to hi h frequency transmlss on is illustrated in ig. 5, in which the original signal and a carrier frequency from ,an oscillator O, are together. impressed upon a modulator M,. A band pass filter ma be introduced to permit the transmission o one side band only,'and this side bandobviously may be impressed upon a converter shown rectly upon an antenna 52, and the other group, after modulation in a modulator M,

with which there is associated a modulator generator 0 could then be impressed upon 7 an antenna 53, the carrier frequency for this second antenna bearing any desired relation to that of the antenna 52. The two antennae could radiate. on the same carrier frequency p, the one transmitting one side band from p to ;0-F/2 and the other band adjacent to it from p to p+F/2. In this case taining secrecy, whichcomprises breaking the signal into, elements, displacing alternate elements into one frequency band, displacing the remaining element into another frequency band adjacent thereto, superposing these on a transmission channel, receiving and separat ng the two portions, and restoring the elements to their normal frequency and normal time relation.

3. In a signaling system the method of;

obtaining secrecy,.which comprises breaking the signal into elements, displacing alternate elements into one frequency band of narrower frequency width, displacing the remaining elements into another frequency band of narrower frequency width, superposing these on a transmission channel, receiving and separating the two portions, and restoring the elements to their normal fre' quency and normal time relation.

LIn a signaling system the method of obtaining secrecy, which comprises breaking the signal into elements, displacing alternate elements into one frequency band of narrower frequency width, displacing the remaining elements into another frequency band of narrower frequency width and immediately adjacent thereto, superposing these on a transmission channel, receivlng and separating the two portions, and restoring the elements to their normal frequency and normal time relation. I

5. In a signaling s stem the method of obtaining secrecy, whic comprises breaking the signal into elements, displacing alternate elements into one frequency band of narrower frequency width, displacing the remaining element'into another frequency band of,

narrower frequency width and immediately adjacent thereto, the bands together occupying the original frequency band, superposing these on a transmission channel,- receiving and separating the two portions, and restoring the elements to their normal frequency and normal time relation.

6. In a signaling system the method of distorting the signal for the purpose of secrecy, which ,consists in interrupting the signal into elements of equal time length, reducing the. frequency and the frequency band width of alternate elements to occupy a lower portion of the normal signaling frequency band, increasing the frequency and reducing the frequency band width of the remaining elements to occupy an upper portion of the normal signaling frequency band, superposing these on a transmission channel, receiving and separating the two portions, and restoring the elements to their normal frequency and time relation.

7. In a signaling system the-method of distorting the signal for thepurpose of secrecy, which consists in interrupting the signal into elements of equal time length, reducing the frequency and the frequency band width of alternate elements to occupy a lower half of the normal signal fre uency mal signaling frequency band, superposing these on a transmission channel, receiving band, increasing the frequency and re ucing and separating the two portions, and restoring the elements to their normal frequency and time relation.

8. In a signaling system the method of ob- Y superposing these on a transmission channel, 1

recelving and separating the two portions of the resultant wave, increasing the freuency and the width of frequency band of t e one portion to normal, decreasing the frequency and increasing the width of frequency band of the other portion to normal, and restoring the elements to normal time relation with respect to each other.

9. In a signaling system themethod of obtaining secrecy, which comprises interrupting the signal into elements of equal time length, reducing the frequency and the fre- 1 quency band width of alternate elements to.

occupy the lower half of the normal signaling frequency band, modulating the 'remaining elements'to a carrier frequency and reducing its frequency and frequency band to occupy the upper half of the normal signalmitting station,

ing frequency band, superposing these on a transmission channel, and restoring the elc ments to their normal frequency and normal time relation.

10. In a secrecy signaling system a transmitting station, a source of signaling current, means at said station for breaking said signal into elements and for decreasing the width of the frequency band of each element,

means for transferrino alternate elements to a frequency band different from that of the other elements, a receiving station, and means thereat for restoring the distorted signal to normal condition.

11. In a secrecy signaling system a transmitting' station, a source of signaling cur: rent, means at said station for breaking said signal into elements and for decreasing the width of the frequency band of each element, means for modulating alternate elements to a frequency band different from and adjacent to that of the other elements, means for superposing the modified alternate elements for transmission, a receiving station, and means thereat for restoring the distorted signal to normal condition.

12. In a secrecy signaling system a transa sourceof signaling current, means at said station for breaking said signal into elements and for decreasing the width of the frequency band of each element, means for modulatirw the alternate elements to a frequency band different from and adjacent to that of the other elements, means for super-posing the modified alternate elements for transmission, means thereat for separating'the two groups of elements, means for demodulating the modulated elements, and means for, expanding the elements to normal frequency and bringing them into normal time relation.

13. In a secrecy signaling system a transmitting station, a source of signaling current, means at said station for breaking said signal into elements of equal time duration and of double duration and half frequency, separate paths for the alternate elements, a modulator in one path adapted to yield a modulated side band adjacent to the frequency band of the other group of alternate elements, means for superposing the two wave portions in transmission, a receiving station, and reclprocal means thereat for re-- converti the received wave into the original signiif In testimony whereof, I have signed my name to this specification this 11th day of 7 August, 1926.

ALLEN CARPE.

a receiving station and' 

